RF transmitters are used for a variety of purposes, such as, for example, broadcast radio and handheld communication devices. It is sometimes desirable to determine when RF transmitters are in use. Law enforcement officials, for example, may want to track or locate an RF transmitter as part of a criminal or terrorist investigation. Investigating the unauthorized or unintentional transmission of RF signals is another application where it is desirable to detect the use of an RF transmitter.
A signal may not be detected by traditional techniques if the transmitter is located some distance away. Signal power decreases with distance, so detection is dependent on the signal-to-noise (SNR) requirements for the signal detection device and the distance to the signal source. Most detection and geolocation techniques require a positive SNR at the detectors.
The techniques may also require a continuous signal or a signal that appears on a regular basis. Some RF transmitters such as low-power walkie-talkies or Family Service Radios transmit an RF signal for a limited amount of time and at random times. These short signal bursts can make it difficult to detect or geolocate the RF transmitter.